1. Field of the Invention
The invention relates to a drill bit and a method for grinding a drill bit having two major cutting edges connected via a chisel edge, adjacent to each of which major cutting edges is a clearance face that transitions into a flute.
2. Background Information
Such drill bits are used for, among other things, twist drills in which the chips removed by the drill bit are removed via flutes in the drill that run in a spiral pattern. For this purpose, the drill bit and drill are designed in one or two pieces. In the two-piece design, the drill bit is realized in particular in the form of a replaceable insert for a drill base element.
The geometric configuration, and especially the grinding of the drill bit, determines to a significant extent the cutting action of the drill and the mechanical load on the drill, especially on the drill bit. The mechanical load during drilling is also determined by, among other things, the configuration of the area around the chisel edge. To reduce the load, the chisel edge is therefore generally pointed during grinding. With pointing, the rake angle is determined in the area of the drill core, which defines the angle between the surface adjoining the chisel edge and the longitudinal axis of the drill. This surface is referred to below as the chisel edge surface. The rake angle in the area of the chisel edge facing away from the major cutting edge is determined, in particular, by where the clearance face associated with the cutting edge transitions into the flute. A positive rake angle is often desired in this area. A positive rake angle means that the chisel edge surface is tilted toward the longitudinal axis of the drill, so that a type of overhang is formed. On the other hand, with a negative rake angle, this surface is tilted away from the axis of the drill.
In conventional grinding methods with pointing, the major cutting edges and the chisel edge, as well as the clearance faces adjoining the major cutting edges, are ground in a first process step. The pointing is then carried out in a second working step. For this purpose, it is essential that the grinding wheel used for the grinding be reset. Consequently a ridge, i.e., a discontinuity, is ground into both the clearance face and the chisel edge surface. The ridge in the chisel edge surface is necessarily formed because, under all circumstances, the grinding wheel must be prevented from reaching the chisel edge already ground during pointing. In the area of the chisel edge, this ridge causes stress peaks that lead to increased loading on the drill bit.
More recent development trends have attempted to produce drill bits without grinding via a metal injection molding process.